This invention relates to hypodermic needles. In particular, it relates to the protection of people using syringes with needles to withdraw samples from the bodies of other people or animals or to inject materials into the bodies of other people or animals.
Health professionals and others who use hypodermic needles to inject medicine or other substances into the bodies of other people or to obtain samples of blood or other bodily fluids from people are subject to a risk of infection if they are stuck with a contaminated needle that has been withdrawn from an infected person. This is a matter of special concern when facing the possibility of dealing with people who have infectious hepatitis or acquired immune deficiency syndrome (AIDS), but it is preferable to avoid or minimize the possibility of infection with any disease. The needle in a hypodermic, being sharp to penetrate the skin readily for its intended purpose, is a threat to penetrate clothing and rubber gloves of the health professional using the hypodermic and thus to puncture the skin of the health professional. The threat of contamination is present with needles that are used for subcutaneous and intramuscular injection, but it is particularly threatening with needles used for intravenous injection of fluids and for the drawing of blood or other body fluids from veins or other parts of the body.
A hypodermic or hypodermic needle is here defined as a combination of a needle, a hub, and a syringe. The needle is attached to and passes through the hub, which in turn attaches to the syringe. If the hypodermic is designed for injection or withdrawal using positive pressure or vacuum produced by a plunger, then the needle is normally terminated after it has passed through the hub, and the syringe is designed to contain fluid and to make a sealed sliding engagement with the plunger. In this case, the plunger is an additional part of the combination representing the hypodermic, and the syringe is typically marked with graduations to measure quantities of fluids injected or withdrawn. If the hypodermic is designed for use in a vacuum withdrawal system, then the needle is normally double-ended, passing completely through the hub and extending beyond the hub in both directions. The syringe in this case does not contain fluid, but instead serves as a guide and support for a vacuum bottle with a soft plastic that is pierced by the needle to apply a vacuum to the needle when withdrawing samples. In either event, the hypodermic is normally equipped with a removable needle cover to protect health professionals from accidental contact with the point of the needle.
For any of the uses described above, universal practice is either to discard the needle after one use, or else to sterilize it before another use. This is done either by inserting the used needle in a cutting dispenser which cuts the needle from its hub and receives the cut needle, or by replacing the needle cover that was removed to ready the needle for use and removing the needle and hub from the body of the syringe to discard the combination of needle and cover. When the needle is inserted in a clipping device, the contaminated point is exposed between use of the needle and its insertion into the clipping dispenser. Carelessness on the part of the health professional or other user of the hypodermic, distractions occasioned by telephone calls and the like, or accidental jostling by passersby, all make it possible to bring the contaminated point of the needle into contact with the body of the health professional. A particular threat exists when the needle cover is replaced before the needle is discarded. In this case the health professional typically holds the needle cover in one hand and inserts the needle into an opening in the cover. The same distracting factors may cause the contaminated point of the needle to come into contact with his or her hand.
The threat described above has been the subject of several patents. Strauss, U.S. Pat. 4,664,654, "Automatic Protracting and Locking Hypodermic Needle Guard" is an example of one means for protecting the tip of a contaminated needle. Strauss teaches a sliding member that covers the needle. The sliding member can be locked in place to protect the point of the needle from coming in contact with anything. When the sliding member is unlocked, the tip of the needle and a portion of the needle are exposed for use. The sliding member is placed against the skin after the needle has made an initial penetration, and the sliding member is pushed back by the skin as the needle is inserted. The spring maintains force on the sliding member, and restores it to the protective position when the needle is withdrawn and the sliding member is removed from the surface of the skin. The sliding member is not locked in the open position. The device taught by Strauss has the disadvantages of being relatively complex mechanically, which increases its manufacturing cost, and also of coming in contact with the skin of a patient. This presents the possibility of contamination of the tip of the needle cover. In addition, the device taught by Strauss is adapted for subcutaneous and intramuscular use but would be difficult to use for intravenous injection or for the drawing of blood samples.
Mitchell, U.S. Pat. 4,631,057, is entitled "Shielded Needle". Mitchell teaches a shield that is concentric with and slides on the body of a syringe. When the shield is advanced to its farthest position in the direction of the needle, the needle is protected by the shield, which can be locked either in an open or closed position. A similar construction is taught by Sampson et al., U.S. Pat. 4,425,120, entitled "Shielded Hypodermic Syringe." The shield of Sampson et al. is locked by turning the shield to engage a detent in a slot. Each of these devices has the disadvantage of covering the body of the syringe when the needle is exposed, as it would be when the user of the syringe is drawing a measured quantity of medication from a vial. The necessity of reading volume marks through the shield represents a disadvantage of the constructions of Mitchell and Sampson et al.